1. Field of the Invention
This invention relates to a device for determining the levelness of compound strings or string sets, namely bichords and trichords, of a grand piano. The device uses the upper surface of the key bed of the piano as a reference surface and determines levelness of the aforesaid string sets. In addition to the string leveling device, a method of use thereof is provided.
2. Description of the Prior Art
The history of the modern piano begins with the pianoforte developed by a harpsichord builder, Bartolommeo Christofori. Christofori invented the instrument in Florence in 1709 and completed a prototype around 1720. The main driving force behind the instrument's development was that, in contradistinction to the predecessor instruments—the harpsichord and the clavichord—the piano provided variations in volume. Additionally development was spurred on by the desire to play fuller, less delicate music.
Musicians of the time sought a full rich sound and were unsatisfied by the strong and uniform harpsichord tone produced by plucking large strings with keyboard-controlled quills. On the other hand, the percussive action of the clavichord, while allowing for variations in volume, produced weak tones by striking brass hammers against small, thin strings.
Of the several versions of the piano invented in the Eighteenth century, Christofori's pianoforte, is most closely related to the modern-day grand piano in that the hammers thereof are wooden blocks covered on the striking surface with soft leather. Later in the Eighteenth century a piano hammer was designed with the same basic shape that survives today. In this design, two layers of leather were used with the inner layer being a firm leather, and the outer layer being softer. The final form of the leather covered piano hammer used three layers of leather of varying firmness with the softest leather on the outside and the firmest layer on the inside. This provided a piano hammer that was soft and compliant at the surface to provide the requisite tone for pianissimo playing and a hammer firmer underneath to provide the strength for forte playing.
As the grand piano developed, it became more and more a solo instrument, and needed to be louder. To increase volume, strings needed to be thicker and the support structure stronger, so that greater tension could be achieved. The frame of the pianos, commonly made of wood, became thicker and heavier, and was strengthened by cross-bracing. By 1820, English manufacturer John Broadwood began to build iron hitch pin plates, which now meant plates were made of more metal than wood. In 1825 Alpheus Babcock patented the cast-iron frame and further in 1843, American manufacturer Jonas Chickering began making pianos with the full-perimeter plate—a feature of modern grand pianos.
In 1821 a French builder, Sebastian Erard, invented the last major basic refinement of the piano action; the double escapement. Shortly thereafter, the heavy iron frame required by the action and the higher tensioned strings was provided, and then cross-stringing, a system whereby the long bass strings cross over the shorter middle-range strings, was invented.
After the invention of the iron frame for the strings on a piano, heavier strings, including bichords and trichords, could be used at higher tensions to produce a fuller sound from the piano. This rendered the leather covered piano hammer unacceptable. The result was the development and patenting of a felt covered piano hammer by Alpheus Babcock in 1833. These hammers provided a more acceptable tone than the leather covered hammers. In the late Nineteenth century machines were invented to cover the raw wood piano hammers with felt. The felt hammers enabled the manufacturer to fine tune the tone of the piano by adjusting the hardness of the felt. The process of tonally regulating the piano hammers is called voicing, requires skilled piano technicians, and is a time consuming operation. Initially, the piano hammer felt is checked for proper shaping, particularly that the striking surface is flat across the width thereof. During voicing, the technician adjusts the tone of a hammer by adjusting the softness or the hardness of the hammer felt. When a tone sounds too soft, by applying a solution of lacquer and lacquer thinner to the hammer felt the technician adjusts the felt hardness and the tone produced at that site. Alternate methods of adjusting hammer felt hardness include working the hammer felt with a needle to loosen the fibrous structure thereof.
String leveling of a grand piano is a process completed before voicing or the adjustments of the felts of the hammers. If the string sets—bichords and trichords—are not level, the strike of the corresponding hammer produces a fuzzy note and the damping of the strike is not properly accomplished. This creates what is referred to as an aftersound or ring, which, in turn, destroys the normal clarity or definition of individual notes of the instrument. In practice, piano technicians are trained to detect unlevel string sets by ear. Upon detection, the technician is presently taught to correct the condition by withdrawing the piano action and placing the end of a steel rule on the string set to sight along the string. When gaps are present, the sagging string is drawn up to the higher string by shortening or kinking the string.
A complete piano action consists of thousands of parts and weighs on the order of 30 kilograms or more and hence has a substantial support or key bed on which the action rests when in the piano case. The key bed is rigidly connected to the piano case and is an integral part of the piano case. Because a mechanical coupling exists between the key bed and the piano soundboard through various components of the piano case, vibrations originating at the key bed are transmitted through the frame of the piano to the soundboard to produce extraneous noise, such as the aftersound, supra, which detract from the tonal integrity of the instrument. Consequently, in a grand piano, as the frame of the piano action is in intimate contact with the key bed, it is critical that the key bed be perfectly flat and that the string sets be precisely level with respect thereto.
There are two other aspects of the grand piano manufacture and maintenance that are impacted by string leveling—the una corda pedal action for playing pianissimo and the damping mechanism for curtailing and ending the resonating of a string set. The una corda pedal in the modern grand piano is the left pedal and shifts the piano action sufficiently in the key bed to enable the piano hammers to strike only one string of each bichord unison and two strings of each trichord unison. This places a further requirement on key bed construction to permit a noiseless sliding of the piano action relative to the key bed whenever the una corda pedal is depressed. The description of the una corda pedal and the action thereof is found in a patent to Harold A. Conklin, Jr., U.S. Pat. No. 4,127,051, which description is incorporated herein by reference.
In the grand piano, the damping mechanism curtails and ends the resonating of a string or string set. The depressing of a key raises a damper wire which, in turn, supports a damper head and the attached damper felt and thereafter, upon release, the damper assembly falls on the string or string set. For even damping across the entire range of the piano, the weight of the damper assembly is varied in accordance with the size and tension of the string or string set so as to have a correspondingly even damping influence on the resonance thereof. The damper felt has a longitudinal aspect which for proper damping action needs to be in full contact with the string or string set. At a pre-determined node when a string set is not level, the damping mechanism does not seat properly thereon and results in a partially damped note. This is created by one or two strings ceasing to resonate and by the remaining undamped string sustaining the note until the natural decay occurs.
In manufacturing a grand piano the process of string leveling is accomplished prior to voicing which was described by Franz Mohr of Steinway as open work (or work with the piano action withdrawn from the piano case). The manufacturer anticipates that during the initial period of use, the instrument will be tuned, string leveled and voiced with greater frequency. This results as the outer portion of the hammer felts continue to be further shaped by the initial play by the pianist. Additionally, the tuning-string-leveling-voicing process takes on particular importance when a pianist individualizes the grand piano for concerts or recording sessions. When voicing is attempted without the pre-requisite string leveling, the shaping and the hardening of hammer felts do not provide the desired clarity as a hammer strike on an uneven string set produces tones with differing decays.
Similarly, in regulating the mechanical arrangement of the una corda pedal, unlevel strings create a condition in which the hammer strikes, instead of squarely meeting the string (bichord) or string set (trichord), are frequently glancing blows. This produces an uneven tonal quality that is readily heard because of the pianissimo mode.
The effect of unlevel string sets when adjusting the damper mechanism is described in a December, 2002 article in the Piano Technicians Journal. Andrew Remillard in an article entitled Dampers: Peace and Quiet at Last indicates that for proper adjustment of the dampers the strings need to be level because, “if one string hangs a little beneath its neighbor it will be virtually impossible to ever completely dampen it.”
Prior to preparing this application, the inventor became familiar with several patents concerned with grand piano manufacture and maintenance, which patents are included herein as further background material. The patents are:
ITEM NO.U.S. PAT. NO.INVENTORISSUE DATE1.6,559,369GilmoreMay 6, 20032.6,489,548SchindlerDec. 3, 20023.6,479,738GilmoreNov. 12, 20024.6,278,047CumberlandAug. 21, 20015.6,107,556GilliamAug. 22, 20006.5,756,913GilmoreMay 26, 19987.5,654,515YouseAug. 5, 19978.5,528,970ZacaroliJun. 25, 19969.5,423,241Scarton et al.Jun. 13, 199510.5,065,660de BudaNov. 19, 199111.4,253,374WattermanMar. 3, 198112.4,127,051Conklin, Jr.Nov. 28, 197813.3,675,529Van Der WoerdJul. 11, 1972
Additional background information was obtained from several nonpatent references, namely:    14. 40TH Annual PTG Convention (1997)—Mini Technical Classes—Michael Vecchione, Making Unisons Sound SPOT ON     15. 40TH Annual PTG Convention (1997)—Mini Technical Classes—Clair Davies, String Leveling     16. 1998 www.ptg.org—John Woodrow, String Leveling Questions     17. Del Fandrick, RPT, Q. and A. On the Level, Piano Technicians Journal (PTJ), Vol 38, No. 2 (1995)    18. Clair Davies, RPT String Leveling by Ear, PTJ. Vol. 40, No. 11 (1997)    19. Solution for Agraffe Noise, PTJ, Vol. 32, No. 8 (1989)    20. Q. and A. Fuzzy, False Tone, PTJ, Vol. 29, No. 3 (1986)    21. Virgil E. Smith Criminal Negligence in Piano Service, PTJ, Vol. 36, No 10 (1993)    22. David W. Pitsch, RPT, After Touch, PTJ, Vol 25, No 12 (1982)    23. Susan Graham, Agraffes, PTJ, Vol. 27, No. 5 (1984)    24. Selections from Five Lectures on The Acoustics of the Piano Proceedings of the Royal Swedish Academy of Piano (1990) as published at www.speech.kth.se
In addition to the patents uncovered, the nonpatent references, as cited above, uncovered a series of five lectures entitled, The Acoustics of the Piano, sponsored by the Royal Swedish Academy of Music (1990). While there was some emphasis on aftersound and the physics of sound upon a hammer striking a string, there is seemingly no mention of the effect of unlevel strings on the voicing or on the damping mechanism. In fact, the discussion seems to indicate that some roughness at the edge of the notes was deliberate, which teaches away from the precise string leveling, infra.
In Clair Davies teaching before the Piano Technicians Guild (PTG) convention about string leveling, he uses the square end of a steel rule to check that the strings are coplanar and does not use the key bed as reference. This teaching also indicates that Franz Mohr called string leveling part of the “open work” of piano tuning.
With the foregoing background in mind, the purpose of the present invention is to provide a novel string leveling device which precisely gauges the condition of the bichords and trichords of a grand piano with reference to the upper surface of the key bed. The disclosed invention also encompasses a method of using the apparatus as a preliminary step to voicing a grand piano, adjusting the damping mechanism and regulating the una corda pedal.